Uh, I believe Cmd-Shift-4 saves the image directly to the desktop, then I usually hit one of my hot corners that shows the desktop, grab it, hit the corner again and drop in the image. It's usually pretty quick. I did not know about holding Ctrl copies the file, I'll probably use that more often now because it probably is a little faster. But if you want to save an image you don't have to open up preview to save it or anything.